The present invention relates generally to irrigation water supply. More particularly, the present invention relates to an improved barbed fitting for use with low density polyethylene irrigation pipe and the like.
Low density polyethylene pipe has been used as a water conduit in special applications for decades. Low density polyethylene pipe is generally flexible and extremely resilient, is capable of withstanding working pressures of 100 PSI and greater and is not reactant in most environments. Because of resilience, low density polyethylene pipe has been the pipe of choice for use in irrigation systems, particularly as a subterranean riser.
Typical PVC supply lines for irrigation systems are installed in a trench, with only the tops of sprinkler heads exposed above grade. An in-line connection is installed in the PVC supply line for each sprinkler, the connection is combination fitting (usually a threaded T-fitting) having at least one PVC slip joint and a threaded joint for coupling a sprinkler head or the like. In a typical irrigation system installation, lawn sprinklers are connected to the PVC supply pipe via a vertical riser pipe and the supply pipe lines at the bottom of the trench. The vertical riser is connected to the threaded T-fitting on the PVC pipe and another pipe thread on the sprinkler. The sprinklers are positioned directly over the rigid riser and the PVC supply pipe, and the trench is backfilled with the sprinkler head exposed. Although this is an extremely efficient installation technique, it suffers from a high instance of post installation pipe damage because of the configuration. After installation, if pressure is placed on the sprinkler head, such as by a person walking on the sprinkler or a vehicle driving over it, the force of the weight is transferred vertically through the traditional riser (from the sprinkler) and is absorbed by the PVC pipe and connection fitting. This often results in a catastrophic breakage of the PVC pipe at the fitting, the fitting itself or both.
This problem is overcome by replacing the riser in the installation with a flexible swing pipe of low density polyethylene pipe that will absorb much of the downward force from a pedestrian, lawn mower, golf cart or even a vehicle on the sprinkler. In a typical installation, a polyethylene swing pipe is connected between a pair of adapters such that the sprinkler head is not positioned directly over the PVC supply line, therefore, these adapters are usually in a Tee or ell (elbow) configuration. Flexible polyethylene pipe will not accept pipe threads and hold the working pressure of an irrigation system. Therefore, polyethylene pipe must be connected to an adapter with threaded and barbed ends. The threaded end of the adapter screws into threaded sprinkler and/or threaded in-line Tee-fitting pipe just as the riser. The barbed end has angled barbs that grab and hold on to the inner surface of the polyethylene pipe and is forced into the polyethylene swing pipe. Barbed fittings are inexpensive and form a watertight and permanent seal without using glue or pipe clamps.
The barrel of the barbed end of the adapter has an outer diameter that is slightly larger (nominally 0.5 inch) than the inner diameter of the polyethylene swing pipe (nominally 0.49 inch) with several circular rows of angled barbs that protrude from the barrel between 1/16 inch (0.0675 inch) and 3/16 inch (0.1875 inch). During installation, the barbed end is manually forced into polyethylene swing pipe, usually by an inch or more, to ensure a water tight and permanent connection to the swing pipe. Often, the amount of force necessary to seat the polyethylene swing pipe around the barb is significant. Thick-wall and high pressure swing pipe are particularly problematic as they are usually much more rigid than standard-duty polyethylene swing pipe. Even standard-duty pipe can be difficult to seat in temperatures below 50° F.